US 20050179623 A1
Driver system (10) for use in connection with a non-linear display array having N×M pixels. The driver system (10) comprises an input for receiving column data representing an image to be displayed, and a row driver designed to sequentially collect the currents of all M pixels of each row of pixels row electrode by row electrode. A gamma correction unit (17) is employed that provides for a gamma correction of the column data. The gamma correction unit (17) is situated at the input side of a display data memory (14) for storing the gamma corrected column data. The driver system (10) further comprises a column driver (24) designed to apply column signals to all M column electrodes in parallel, the column signals being generated in accordance with the gamma corrected column data.
1. Driver system for use in connection with a non-linear display array having N×M pixels, the driver system comprising
an input for receiving column data representing an image to be displayed,
a row driver designed to sequentially collect the currents of all M pixels of each row of pixels row electrode by row electrode, by applying a row select signal to the N row electrodes so as to scan the rows of pixels one after the other,
a gamma correction unit providing for a gamma correction of the column data,
a display data memory for storing gamma corrected column data,
a column driver designed to apply column signals to all M column electrodes in parallel, the column signals being generated in accordance with the gamma corrected column data.
2. Driver system of
N row electrodes,
M column electrodes, and
N×M light emitting diodes, each light emitting diode having an anode and a cathode, the light emitting diodes being arranged in N rows and M columns.
3. Driver system of
4. Driver system according to
5. Driver system according to
6. Driver system according to
7. Driver system according to
8. Driver system according to one of the preceding claims, further comprising a pulse control unit which renders it possible to display different grey levels on the display.
9. Driver system according to one of the
10. Nonlinear display array comprising a driver system according to one of the
11. Polymer light emitting diode array comprising a driver system according to one of the
The present invention relates to non-linear display systems, such as polymer light emitting displays that require a random access memory for storing static image content, and in particular drivers for displays of this kind.
With the widely divergent use of electronic devices comprising displays, for instance laptop computers and mobile phones, various display technologies have been employed, for example liquid crystal displays (LCD), light emitting diode (LED) displays, and more recently organic light emitting (OLED) displays.
Cathode ray tubes (CRT) and thin film transistor (TFT) matrix displays are further examples of display technologies widely used. Since CRT and TFT displays have a non-linear characteristic, a gamma correction is performed in order to adjust the image being displayed accordingly. These displays are mostly employed in devices where the display content changes dynamically and there is thus no need for a display data memory.
The OLED technology holds promise because of its ability to efficiently address a very wide range of colors, while operating at extremely low power. As a result, this technology is expected to be brighter, lower in cost, consume less power (which is an advantage if used in portable electronic devices which depend on a battery as a power source), afford wider viewing angles, and be extremely lightweight. OLEDs are thus ideal for today's mobile device applications. Moreover, this technology will be also ideal for a variety of lighting conditions and capable of running at fill speeds in extreme temperatures.
Polymer light emitting diodes (PolyLED), a segment of the total OLED market, will be a key display technology in the future, especially in color mobile applications.
Some of the essential parts of a conventional matrix driver 1 are illustrated in
The power consumption of current display drivers for use in connection with non-linear displays is still an issue, and there is a demand for display devices consuming even less power than conventional ones.
It is an object of the present invention to provide an improved driver for a non-linear display and to provide an improved non-linear display device.
It is an object of the present invention to provide a driver for non-linear display, e.g. an electroluminescent display, that consumes less power than a conventional driver.
These and other objects are achieved by the present invention, which provides a driver system for use in connection with a non-linear display array. The driver system comprises a row driver designed to sequentially collect row-by-row the currents of the pixels of a row. This is done by applying a row select signal to the N row electrodes to scan one row after the other. A gamma correction unit is employed for performing a gamma correction of column data representing an image to be displayed. The gamma corrected column data are stored in a display data memory. The driver system comprises a column driver designed to apply column signals to the M column electrodes in parallel, the column signals being generated in accordance with the gamma corrected column data.
Also provided is a non-linear display (for example a passive matrix N×M polymer light emitting diode array) comprising a driver system.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.
For a more complete description of the present invention and for further objects and advantages thereof, reference is made to the following description, taken in conjunction with the accompanying drawings, in which:
The present invention is described in connection with several embodiments. In the following sections mainly polymer OLED (PolyLED) color display are being addressed. The invention, however, is also applicable to any other type of non-linear display array.
A driver 10 in accordance with the present invention is illustrated in
An example of a monochrome PolyLED display 40 is depicted in
The driver 10, as illustrated in
In the present example, the buses 15 and 16 are 16 bits wide. According to the present invention, a gamma correction unit 17 is employed. This unit 17 is situated in front of the display data memory 14 and is designed to transform the column data received via bus 15 into column data that take into consideration the non-linear behavior of the light emitting diodes of the PolyLED display 40. Such a gamma correction is necessary since the relationship between the current fed through a diode and the brightness of the light emitted by the diode is non-linear. An exemplary current versus brightness curve is given in
These gamma corrected data are then fed via the bus 16 into the memory 14. Optionally, data latches 18 are employed at the output of the memory 14 to keep the gamma corrected column data for a short period of time. The gamma corrected column data are forwarded in several steps via the buses 19, 20, and 21 and the units 18 (optional) and 23 to a column driver 24. The buses 19 to 22 are 128×3 bit wide. A pulse control unit 23 is situated at the output side of the RAM 14. This unit 23 transforms the data representing the three colors green, red and blue into corresponding grey levels. This may be done by controlling the length w of the column signals c1(t)-c6(t), for example. By doing so, the time a row is selected (active) and is divided into small slots which may be a fraction of the slot lengths depicted in
There is a column driver 24 comprising switches (for example MOS transistors or bipolar transistors). These switches are employed to switch a current Icol received from a current source 25. It is possible to calibrate the current Icol via the input 26. Other than an LCD display which is driven with voltage levels, the PolyLED display 40 is driven with constant currents. An example of a switch suitable for use in connection with the present invention is described in the PCT-patent application WO 99/65012, as published on 16 Dec. 1999. This PCT-patent application is currently assigned to the assignee of the present application.
A converter block 27 in provided for up- or down-conversion of the supply voltage Vdd2 to the voltage Vh needed by the display 40 (in the present example, Vh=3.3 volts). The supply voltage Vdd2 may be provided by a battery. An oscillator 28, for example an RC-oscillator, provides the timing signal needed by a timing controller 29. The timing controller 29 synchronizes the column signals c1(t)-c6(t) and the row select signal r(t). For this purpose, the timing controller 29 is connected via links 30 and 31 to the RAM 14 and the row driver 32, respectively. The row driver 32 comprises switches (for example MOS transistors or bipolar transistors) that connect to the row electrodes of the display 40.
It is an advantage of the present invention that gamma correction of incoming column data is only needed when the image on the display 40 changes.
According to the present invention, a gamma correction unit 17 is, for example, a logic block implementing a non-linear function. Its input received via the bus 15 is a number represented with N bits (for example N=16) for a pixel color content. The output at the bus 16 is a number represented on M bits (for example M=18) where M may or may not be equal to N. The output number M sets the exact length of the current pulse, created by the pulse control unit 23. The pulse control unit 23 is fixed (wired-up), whereas the gamma correction unit 17, according to the present invention, allows a certain degree of programmability, either to adapt to a specific electroluminescent material or to cope with the material's efficiency degradation in time.
In detail, the gamma correction unit 17 may be, in a preferred embodiment, a look-up table, but not exclusively: any digital processing unit with an N-bit number as input and an M-bit number as output and mimicking the non-linear characteristic of the display (cf.
In a preferred embodiment of the present invention, the gamma correction unit 17 comprises a look-up table. The column data can be converted while being written into the RAM 14. The advantage is that this look-up table is addressed while the column data are being transferred or changed only if a change is necessary. Otherwise the content of the RAM 14 remains static. As long as the image on the display 40 remains static, no gamma correction needs to be performed. The gamma correction is only carried out when new column data are received via the input 1, and not during each time slot, as in a conventional driver illustrated in
The inventive approach saves computing logic, time and power, since each gamma correction would consume power.
Another embodiment is characterized in that a timing generator is employed that generates unevenly distributed time slots w(t). An example of a current vs. brightness curve 50 is depicted in
In another embodiment, a separate unit is provided before the display data memory in order to provide for a compensation of the degradation of the light emitting diodes. There is a correlation between the current flowing through the individual diodes and their efficiency. An analytical expression of the relationship of the current vs. light output may be used to determine an additional charge to be injected into a particular LED for it to maintain a (substantially) constant light output. A look-up table, preferably a table sampled in time, may be comprised in the separate unit in order to account for this degradation before storing the column data in the display data memory.
The driver according to the present invention offers an integrated DC-DC converter and oscillator, multiple serial and parallel high-speed bus interfaces, and an integrated gamma correction solution that is fast and efficient.
Drivers in accordance with the present invention can be used in small-scale mobile applications including cellular phones, pagers, digital cameras, PDAs, and so forth.
It is appreciated that various features of the invention, which are, for clarity, described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment may also be provided separately or in any suitable subcombination.
In the drawings and specification there have been set forth preferred embodiments of the invention and, although specific terms are used, the description thus given uses terminology in a generic and descriptive sense only and not for purposes of limitation.